參數(shù)資料
型號(hào): TPS40071PWPR
廠商: TEXAS INSTRUMENTS INC
元件分類: 穩(wěn)壓器
英文描述: 2 A SWITCHING CONTROLLER, 1000 kHz SWITCHING FREQ-MAX, PDSO16
封裝: GREEN, PLASTIC, HTSSOP-16
文件頁數(shù): 4/28頁
文件大?。?/td> 655K
代理商: TPS40071PWPR
PROGRAMMING SOFT START
t
START w 2p
L
C
OUT
(5)
t
START v
D
MIN
f
SW
10*7
ms
(6)
C
SS +
12
10*6 A
0.7 V
t
START
(Farads)
(7)
PROGRAMMING SHORT CIRCUIT PROTECTION
ILIM Threshold
T2
T1
ILIM Threshold
T3
T1
ILIM
SW
VIN 2V
UDG03173
Overcurrent
(A)
(B)
SLUS582J – DECEMBER 2003 – REVISED APRIL 2009 .................................................................................................................................................. www.ti.com
TPS4007x uses a closed-loop approach to ensure a controlled ramp on the output during start-up. Soft-start is
programmed by connecting an external capacitor (CSS) from the SS pin to GND. This capacitor is charged by a
fixed current, generating a ramp signal. The voltage on SS is level shifted down approximately 1 V and fed into a
separate non-inverting input to the error amplifier. The loop is closed on the lower of the level shifted SS voltage
or the 700-mV internal reference voltage. Once the level shifted SS voltage rises above the internal reference
voltage, output voltage regulation is based on the internal reference. To ensure a controlled ramp-up of the
output voltage the soft-start time should be greater than the L-COUT time constant or:
To ensure correct start up of the converter, the soft-start time is limited and can be calculated using Equation 6.
where
D
MIN is the minimum operating duty cycle
f
SW is the converter switching frequency
Please note: There is a direct correlation between tSTART and the input current required during start-up. The lower
tSTART is, the higher the input current required during start-up since the output capacitance must be charged
faster. For a desired soft-start time, the soft-start capacitance, CSS, can be found from:
The TPS4007x uses a two-tier approach for short circuit protection. The first tier is a pulse-by-pulse protection
scheme. Short circuit protection is implemented on the high-side MOSFET by sensing the voltage drop across
the MOSFET when its gate is driven high. The MOSFET voltage is compared to the voltage dropped across a
resistor (RILIM) connected from VDD to the ILIM pin when driven by a constant current sink. If the voltage drop
across the MOSFET exceeds the voltage drop across the ILIM resistor the switching pulse is immediately
terminated. The MOSFET remains off until the next switching cycle is initiated. This is illustrated in Figure 10.
Figure 10. Switching and Current Limit Waveforms and Timing Relationship
12
Copyright 2003–2009, Texas Instruments Incorporated
Product Folder Link(s): TPS40070 TPS40071
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